Chinavasion Pico Projector

A Wi-Fi-enabled pico projector that runs Linux? Find out what our Hack Editor thinks of the hackability of this device.

Distribution Wars

As I extracted and tried to run various ARM-compiled Debian binaries on
the projector, a common issue popped up—either my glibc was too new
or too old. The glibc libraries are one of the core libraries for a Linux
system that basically every C program needs to run, and the version this
projector had seemed to fall somewhere between Debian Etch and Debian
Lenny, with binaries from the former not executing and binaries from the
latter complaining about a glibc that was a bit too old. It seemed like
Lenny was the distribution closest to this one, but I honestly am not
sure on what distribution or version this Linux install is based. The
libc-2.3.3.so possibly seems to be from some ARM-compiled Fedora
distribution. In any case, without glibc support, there was basically no
way I could get most of my binaries to run, and I didn't want to risk
bricking the device by overwriting the existing libraries, so I had to
find a different approach.

Chroot and Library Hacking

My next plan was to track down a small Debian Lenny-based ARM
distribution so I could copy the full root filesystem to the 400MB
/mnt/mtd partition. Then, I could just chroot into that and run the
commands I wanted. That way, all the commands would use that glibc, and
I could add extra ARM-compiled Lenny packages. The problem I ran into
fairly quickly was that, well, chroot segfaulted. Both the chroot binary
that was included on the projector and the version in my Lenny install
failed to work.

At this point, I started refreshing my memory on LD_LIBRARY_PATH,
LD_PRELOAD and other variables I could use to tell a binary to use the
version of the libraries under /mnt/mtd that I had installed. It turned
out that got me a lot further. I could launch ls and a number of other
console applications, including useful programs like strace and lsof;
however, fbgetty was abandoned before Debian Lenny, so I had to try
other framebuffer terminal applications in Lenny, such as jfbterm. The
application would start, but it never seemed to be able to attach
to the tty it wanted, and ultimately, it would error out. After trying
a few things, including changing the permissions on /dev/console to be
more permissive, I gave up for the moment and turned off the projector.

Bricked

The next time I turned on the projector, the splash screen started with
its scrolling progress bar, but after a minute or two, the progress bar
seemed to freeze, and the system was unresponsive. Great, I bricked it.
But how? After all, I had just added some files to a basically empty
mountpoint and changed permissions on /dev/console. At least, that's
all I could remember doing. At this point, I wasn't sure what to do. I
didn't want to take apart the device (at least not yet), so I rebooted it
a few times and tried to see if I could get any information. One thing
I thought about was that the system might have needed all that space
in /mnt/mtd that I had filled up or possibly all of my changing of VTs
could somehow have been remembered (even though that seemed unlikely).

At this point, I remembered the init script that automatically
upgraded the device, so I decided to make a USB key with a test script
that would write a file back to the USB drive. If that worked, I could
just continuously boot the device with the USB key and build up a script
that could repair any damage I may have done. Unfortunately, when I tried
this approach, I noticed that the device didn't seem to get very far into
the boot process—the script never seemed to run.

Next, I decided to connect a USB keyboard and see if the system even
loaded the kernel at all. It turned out that the keyboard did work, as
the Caps-Lock key lit and Ctrl-Alt-Del at the right point did reboot the
device. Unfortunately, when the system froze, so did the keyboard. At this
point, I tried all sorts of keyboard combinations during boot to change
the VT back and forth to attempt to Ctrl-C through some script that
may have stalled, and through some sort of magic voodoo, whether it was
something I hit on the keyboard, or as I've come to suspect, something on
the hardware that started working again, finally the system fully booted.

After I breathed a sigh of relief, I realized I needed to make an
immediate backup of the filesystem, so I had some record of what
was there. I also decided to take off the cover to see if I could
find a serial port on the hardware and access the boot prompt and
boot messages. If you look at Figure 3, you can see the bottom of the
motherboard on the device, and at the top of the picture is a small
five-pin white connector labeled Program that I'm assuming is some sort of
serial interface. Unfortunately, this connector is incredibly tiny, so I
haven't been able to track down a compatible connector yet and test this
theory. Figure 4 shows the top of the motherboard—what you would see
if you simply unscrewed and lifted off the top of the projector. One
thing I noticed when I looked on the board was extra soldering points
for an extra USB port and VGA. More-seasoned hardware hackers might
find even more interesting things on the board once they take a
look.

Figure 3. Bottom of the Motherboard

Figure 4. Top of the Motherboard

Unfortunately, after I took it apart, I had the same trouble with a frozen
progress bar at boot. After a number of reboots, I finally was somehow
able to get it to boot completely, but since then, I've experienced the
same issue a few other times. Eventually, the system will boot, but as of
yet, I've been unable to track down the source of the problem. At this
point, I'm leaning toward some sort of short on the device.

Kyle Rankin is a director of engineering operations in the San Francisco Bay Area, the author of a number of books including DevOps Troubleshooting and The Official Ubuntu Server Book, and is a columnist for Linux Journal.

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